This invention relates generally to orthodontic devices. More specifically, this invention relates to orthodontic brackets and particularly self-ligating orthodontic brackets.
Several types of orthodontic brackets have been used in the prior art, including labial brackets and lingual brackets, which can each be either non-self ligating or self-ligating. As the name implies, labial brackets are positioned on the labial surfaces of a person""s teeth. The most conventional type of labial bracket is a symmetric dual-wing bracket as shown in FIGS. 1 and 2. Referring to FIGS. 1 and 2, this bracket 1 has a bonding pad 4, a base member 6, and two opposing wings 12. An archwire slot 10 is located between the two wings 12 and receives an archwire 8 at a right angle to the plane of the bonding pad 4. After the archwire 8 is in place within the archwire slot 10, an O-ring 14 is placed around one of the wings 12 and then stretched over the opposing wing 12 in a single-tie configuration to retain the archwire 8 in place. Because it requires an O-ring to retain the archwire 8 in its slot 10, this bracket 1 is non-self ligating.
The single-tie O-ring configuration used with this bracket 1 allows the elastic tensile forces of both halves of the O-ring 14 to symmetrically oppose a force (represented by arrow 16) tending to remove the archwire 8 from the archwire slot 10. O-rings 14 must typically be replaced at least every six weeks because their elastomeric material degrades over time as a result of the chemical environment of the mouth. When it is time to replace the O-rings 14, the O-rings 14 are removed and replaced one at a time by simply disengaging the end portions of the O-ring 14 from the wings 12. The conventional labial bracket 1 is, therefore, fairly simple to use because the replacement of O-rings is straightforward.
Lingual brackets are attached to the lingual surfaces of a person""s teeth. Lingual brackets are desirable because they are not readily noticeable to an outside viewer. Unlike the labial brackets described above, however, the conventional lingual brackets, as shown in FIGS. 3, 3A, 4, and 4A, are generally difficult or inefficient to use. Referring to FIGS. 3, 3A, 4, and 4A, a conventional lingual bracket 20 is asymmetric and comprises a bonding pad 24, a base member 36, and opposing occlusal (or incisal) and gingival wings 32 and 38, respectively.
The conventional lingual bracket also includes an archwire slot 30 located between the two wings 32 and 38. The archwire slot 30 of these brackets, however, is angled toward the gingival wing 38. The archwire slot 30 has an entrance in the direction of the gingival wing, opposing first and second walls, and a base located opposite the entrance in the direction of the base member 36. Examples are shown in U.S. Pat. Nos. 4,337,037 and 4,669,981 to Kurz. The gingival wing 38 can include an elongated extension with a knob end as shown in Kurz ""981 or can be T-shaped to serve as a hook for inter-maxillary elastics. These lingual brackets are also non-self ligating because an O-ring 34 is used to secure an archwire 26 in the archwire slot 30.
FIGS. 3 and 4 show the most typical tying arrangement of the conventional lingual bracket, i.e., double-tied. Referring to FIGS. 3 and 4, an O-ring 34 is generally double-tied around the archwire 26 of the conventional lingual bracket 20. In a double-tie configuration, the O-ring 34 must first be placed around the base 36 of the bracket 20. Only after the O-ring 34 is positioned around the base 36 is the archwire 26 inserted into the archwire slot 30 in a direction at an acute angle to the plane of the bonding pad 24.
A second end portion of the O-ring 34, located between the gingival wing 38 and the bonding pad 24, is then stretched over the gingival wing 38, around the archwire 26 and back over the occlusal wing 32, forming a substantially U-shaped O-ring configuration, as viewed from a side view. The tensile forces of both halves of the O-ring 34 retain the archwire 26 within the archwire slot 30 by nearly symmetrically opposing a force (represented by arrow 22) tending to disengage the archwire 26 therefrom.
Unfortunately, there are disadvantages with the double-tied lingual bracket of the prior art. First, as with labial brackets, the O-rings of lingual brackets must be replaced frequently. Unlike the single-tied labial brackets, however, the process for replacing the O-ring on a double-tied lingual bracket is complex. To replace the O-ring, the second end portion of the O-ring must first be stretched back over the occlusal and gingival wings such that the O-ring surrounds only the base member. Then, the archwire must be removed from the archwire slot. Only then can the old O-ring be completely removed from the bracket. Finally, a new O-ring must be attached using the steps described above for attaching the original O-ring. This process must be repeated for each of the lingual brackets needing O-ring replacement.
Another serious disadvantage with the use of double-tied conventional lingual brackets is that the O-ring must be stretched much further than that of the labial bracket. Excessive stretching further reduces the life of the O-ring. Furthermore, to accommodate this amount of stretching, the double-tied lingual bracket O-ring must be highly elastic. This increased elasticity adversely affects its tensile strength, and hence its ability to oppose forces that remove the archwire from its slot.
To avoid some of these disadvantages associated with double tying the O-ring of the conventional lingual brackets, a single-tie configuration for the same brackets has been attempted. Although it is possible to single tie the archwire into the archwire slot of the conventional lingual bracket, using a single-tie configuration with the conventional lingual bracket is disadvantageous because it results in a very weak retaining force. FIGS. 3A and 4A show a conventional lingual bracket using a single-tie configuration.
As shown in FIGS. 3A and 4A, in a conventional lingual bracket 20 with a single-tie configuration, the O-ring 34 is placed over the gingival wing 38 and then stretched over the occlusal wing 32. In this configuration, a force (represented by arrow 22) acting to disengage the archwire 26 from the archwire slot 30 is only weakly opposed by the O-ring 34 for several reasons. First, only the portion of the O-ring 34 extending from the occlusal wing 32 has a tensile force which directly opposes movement of the archwire 26 away from the slot 30. The other portion of the O-ring 34, attached around the gingival wing 38 at approximately a right angle to the first portion, is free to slide along the gingival wing 38. It does not, therefore, provide any significant retaining force.
Further disadvantageous is the fact that the O-rings used to single tie the archwire into the archwire slot of the conventional lingual bracket must be replaced more frequently than those used in a double-tie configuration because they only have one portion of the O-ring that directly opposes the force tending to remove the archwire from the archwire slot. These drawbacks associated with conventional lingual brackets have made their use much less desirable than the labial brackets, despite the fact that many people prefer them aesthetically.
U.S. Pat. No. 4,531,911 (xe2x80x9cCreekmorexe2x80x9d) discloses other single-tie bracket configurations for both labial and lingual applications. Creekmore, and the other dual-wing prior art brackets described above, rely solely on tensile properties of the O-ring to retain the archwire within the archwire slot. They do not contemplate the use of other properties of the O-ring which might aid in retaining the archwire within its slot.
The industry has been unable to provide to the orthodontic profession a simple, lingual bracket which allows easy O-ring attachment and replacement while providing sufficient retaining strength. Furthermore, the industry has relied solely on the tensile elastic properties of O-rings to retain the archwire within the archwire slot of both lingual and labial brackets. What the industry needs, therefore, is a lingual bracket which facilitates easy attachment and replacement of O-rings without compromising retaining strength. The profession would also be benefited by a method of retaining an archwire within the archwire slot of a lingual bracket which uses a more stretch-resistant O-ring.
Self-ligating brackets are one way to solve the difficulties that arise from the use of O-rings. Self-ligating brackets avoid the need for O-rings altogether by integrating a ligating member into the bracket itself. U.S. Pat. No. 6,042,374 (the ""374 patent), for instance, discloses a self-ligating bracket that utilizes an integrated ligating member with at least one coil spring segment to secure the archwire within the archwire slot. The ligating member of the ""374 patent is secured to either an occusal or gingival side of the bracket. After the archwire is positioned within the archwire slot, the ligating member is wrapped around the archwire and removably secured by one or more tie wings on the opposite side of the bracket. The coil spring segment allows the ligating member to stretch around the tie wings and bias the archwire in its slot.
Some advantages in lingual orthodontic brackets have been obtained by using camming closures to secure the archwire in the archwire slot, as for example, in U.S. Pat. Nos. 4,443,189; 5,511,976; 5,791,897; and 5,863,199. Each of these brackets have avoided the need for a double-tie O-ring configuration while still strengthening the retention of the archwire in the archwire slot over the conventional single-tie O-ring configuration. Generally, these configurations include a camming arm that closes to secure an archwire in the archwire slot. An O-ring can then be secured around the tie-wing and the camming arm to keep the arm in a closed position. Although these assemblies provide a fairly strong closure that is simpler to use than the double-tie O-ring configuration, these assemblies are fairly complex to manufacture and therefore expensive. They are also still not as simple to use as the single-tie O-ring configuration.
Self-ligating brackets offer distinct advantages over non-self ligating brackets in many treatment situations because of their ease of use. It is even more desirable, however, to be able to easily convert between non-self ligating and self-ligating brackets during treatment of a given patient to allow the orthodonist to choose the appropriate form of treatment at any given time. The ability to convert non-self ligating orthodontic brackets into self-ligating brackets would therefore be beneficial to the industry.
One object of the invention is to enable secure ligation of an archwire in a lingual bracket using a single-tie O-ring.
A first aspect of this invention is a lingual orthodontic bracket and a method of tying that makes tying elastomeric O-ring ligatures on a lingual orthodontic bracket much simpler and more effective. The bracket takes advantage of compression-resistant properties of an O-ring, in addition to its tensile elasticity, to secure an archwire within an archwire slot in a single-tie configuration. To do this, a T-shaped member of the gingival wing is positioned close enough to the archwire slot to provide a choke point that allows a cross-section of the O-ring to be compressed by a dislodging force.
Specifically, the bracket has a base member, which can be connected to a bonding pad. Opposing first and second, or occlusal and gingival, wings are connected to the base member to receive opposite end portions of an O-ring. An archwire slot is defined in the base member between the first wing and the second wing and is angled toward the second wing. An O-ring slot is defined transverse to the archwire slot in a lateral side of the base member between the base member and the second wing and is configured to receivingly engage a portion of the O-ring. The O-ring slot is arranged to form a choke point so that a force tending to remove the archwire from the archwire slot will compress the O-ring cross-sectionally between the archwire and the second wing.
In operation, the archwire is positioned within the archwire slot of the bracket, but a force tends to cause it to disengage from the archwire slot through an entrance thereof. The O-ring is attached between the first wing and the second wing such that the archwire is retained within the archwire slot by the O-ring. According to the preferred embodiment, the O-ring is stretched in a substantially L-shape configuration around the archwire from the first wing to the second wing, with a portion of the O-ring located in the O-ring slot. Thus configured, the O-ring opposes the force tending to remove the archwire from the archwire slot by both a tensile force and a compression resistant force.
A method for removably securing an archwire within an archwire slot of a lingual orthodontic bracket having a base member, opposing first and second wings, and an archwire slot positioned between the wings and canted toward the second wing is also provided. The method includes forming an O-ring slot on a lateral side of the base member between the base member and the second wing. An O-ring is removably attached around the first and second wings and over the archwire located within the archwire slot so that a force tending to remove the archwire from the archwire slot will be opposed by an elastic tensile force of the O-ring. The O-ring is further removably positioned within the O-ring slot such that the force tending to remove the archwire from the archwire slot is opposed by a cross-sectional compression resistant force of the O-ring.
Another object of this invention is to provide a self-ligating mechanism that can be added to a non-self ligating lingual bracket at any time during treatment.
In this aspect of the invention, a self-ligating mechanism replaces the O-ring to secure the archwire into the archwire slot of a lingual orthodontic bracket. The self-ligating mechanism includes an attachment mechanism for removably attaching the self-ligating mechanism to the bracket. According to a preferred embodiment of the present invention, an occlusal-gingival auxiliary slot is milled, molded, or otherwise formed in the base of the bracket to receive an elongated attachment member, such as a pin, to which a self-ligating member, such as a lockwire or bale, is attached. After the bracket is mounted on the tooth, the attachment member is insertable into, and removable from, the auxiliary slot to permit the orthodontist to vary the mode of treatment, as desired. The self-ligating mechanism can be installed, left in place for a number of archwire changes, and then removed for subsequent treatments.
Although preferably configured for use with the lingual bracket described in the first aspect of this invention, this aspect of the invention can be implemented in other lingual brackets by including an occlusal-gingival slot in the base, and inserting an attachment member in a gingival direction into the slot. The attachment member carries a self-ligating member.
In the presently most-preferred embodiment, the pin is constructed of two layers configured to be inserted into the auxiliary slot. A base layer of the pin is configured having an end that protrudes from an occlusal end of the auxiliary slot of the bracket when inserted therein. A resilient layer of the pin is flexibly secured to the gingival end of the base layer of the pin so that it will fit inside the auxiliary slot under compression and allow for controlled sliding of the pin within the auxiliary slot. The protruding end of the base layer includes a hinging member securing a self-ligating member in rotational or hinged engagement with the base. The hinging member can be, for instance, an occlusally-located tube brazed onto an outward surface of the base layer in a mesio-distal orientation or an end of the base layer bent to form a tube shape.
In one embodiment, the self-ligating member is a U-shaped lockwire having a portion transverse to the pin member carried in the tube and having opposing arms extending from the transverse portion along opposite sides the bracket body. The lockwire rotates between a ligating and a non-ligating position. When the tube is brazed, the lockwire is inserted into the tube and then formed to shape. When the tube is formed from a bent end of the base layer, the lockwire can be pre-formed and snapped into place. In its ligating position, the opposing arms of the lockwire extend first along an outside of the bracket body and then bend inwardly into the ligature channels of the bracket to secure an archwire in an archwire slot. The lockwire has indentations that point toward the midline and seat into a gingival extenuation of the archwire slot when the lockwire is fully seated in its ligating position.
The combination of controlled sliding of the base member into the auxiliary slot and rotation of the lockwire permit the complex movement necessary to properly seat the lockwire in the ligature channels of the bracket. Also significantly, since the ends of the lockwire are positioned in the ligature channels in an orientation that is transverse to the archwire slot, a force tending to remove the archwire from its slot creates a shear force on the lockwire. Because the lockwire metal has a relatively high shear strength, this self-ligating mechanism provides very strong archwire retention.